IN VIVO ROLE OF SULFITE IN PHOTOCONTROL OF UROCANASE FROM Pseudomonas putida

Abstract— Urocanase from Pseudomonas putida becomes inactive in growing and resting cells and is activated by UV radiation. Sulfite addition to the bound nicotinamide adenine dinucleotide coenzyme has previously been shown to inactivate the enzyme in vitro. The enzyme released sulfite upon photoactivation. Whether sulfite addition and dissociation is involved in the in vivo photoregulation of urocanase was examined in this study. The dark reversion (inactivation) in cultures was markedly enhanced by growth at 32°C rather than at 24°C; cells grown at 32°C and resting cells were used to obtain in Wvo‐inactivated urocanase. We purified the in vivo‐inactivated enzyme and quantitated the amount of sulfite released through photodissociation. One mole of sulfite was released per mole of urocanase. This is based on a molecular weight of 110000 confirmed by gel electrophoresis and a protein estimation method validated by our data. Our previous report of sulfide inactivation of urocanase in vitro is now shown to have been mistaken; the inactivation resulted from the oxidation of sulfide to sulfite, which occurred in solution.